Detect failed connection

[zbraniecki]

As far as I can tell there's no way to detect a connection failure until an API call is executed.
This means that building a library that wraps around capnweb to handle connection management is tricky as it requires at least one known API to be available to test if the connection succeeded.

I'm not sure if a newWebSocketRpcSession is meant to be lazy or eager, but it would be helpful to expose some state information and maybe an explicit connect call that can succeed or fail.

[kentonv]

You can use onRpcBroken() to detect disconnect proactively:

https://github.com/cloudflare/capnweb?tab=readme-ov-file#listening-for-disconnect

[zbraniecki]

It only captures if the connection is first established, and then disconnected.
My understanding is that the current order is:

1. You instantiate a session (nothing happens, lazy)
2. You execute an API call (connection gets established, or not)
3. After that moment, if the connection was established in (2) the onRpcBroken will be called in case of disconnection

But the session is useful before (2), since the endpoint can call (1) and hope that it will receive calls from the other endpoint.

Right now, there's no good way to verify that except of superfluously calling (2) to verify that the connection is established and capturing the API call failure as lack of connection.

[kentonv]

I don't understand. newWebSocketRpcSession() is not lazy. It initiates the connection immediately, and if the connection fails, then onRpcBroken listeners will be invoked, regardless of whether you invoked any follow-on RPC calls.

If you are seeing something different, can you please provide some example code demonstrating the problem?